Combine coverings

Set operations on a5_covering vectors, computed on the compacted cells without expanding them, so they stay fast for coverings that stand for billions of cells:

Usage

a5_union(x, y = NULL)

a5_intersect(x, y)

a5_difference(x, y)

Arguments

x, y

a5_covering vectors, or objects as_a5_covering() accepts. Sizes must be compatible under vctrs recycling rules.

Value

An a5_covering vector of the common size of x and y (size one for a5_union(x)). NA where either input is NA; a5_union(x) skips NA elements.

Details

• a5_union(): cells in either covering. With y omitted, the union of every covering in x, as one covering: for example the coverings of all features from a5_polygon_to_cells().

• a5_intersect(): cells in both coverings.

• a5_difference(): cells in x but not in y.

The operations work element by element, recycling a length-one argument, so a5_intersect(countries, cap) intersects every country with one cap. Both coverings of a pair must be at the same resolution: A5 cells do not nest geometrically across resolutions, so combining sets at different resolutions has no meaning, and it is an error. An empty covering with no recorded resolution, as a5_compact() returns for no cells, combines with any covering as the empty set.

See also

a5_contains(), a5_overlaps() and a5_count() to query coverings.

Examples

edinburgh <- a5_lonlat_to_cell(-3.19, 55.95, resolution = 12)
glasgow <- a5_lonlat_to_cell(-4.25, 55.86, resolution = 12)
caps <- a5_spherical_cap(c(edinburgh, glasgow), radius = 40000)

a5_union(caps[1], caps[2])
#> <a5_covering[1]>
#> [1] res 12: 4,766 cells (434 stored)
a5_intersect(caps[1], caps[2])
#> <a5_covering[1]>
#> [1] res 12: 195 cells (69 stored)
a5_difference(caps[1], caps[2])
#> <a5_covering[1]>
#> [1] res 12: 2,288 cells (260 stored)

# the union of every element
a5_union(caps)
#> <a5_covering[1]>
#> [1] res 12: 4,766 cells (434 stored)